1. Field
Example embodiments relate to stack-type image sensors, and more particularly, to stack-type image sensors using a resistance change element.
2. Description of the Related Art
Image sensors are used in various fields. For example, high density image sensors may be used in a high definition camera, and image sensors sensitive to ultraviolet/infrared rays may be used in a touch panel. Most commercially available image sensors include a charge-coupled device (CCD) image sensor or a complementary metal oxide semiconductor (CMOS) image sensor. Each of the CCD image sensor and the CMOS image sensor uses a PN junction of a semiconductor material such as silicon.
Recently, research is being conducted in a micro process for highly integrate image sensors. If the size of a chip is reduced by using a micro process, while maintaining the same number of pixels of the image sensors, then more image sensors may be produced from one wafer. Accordingly, the unit cost of the image sensors may be reduced, production of the image sensors may be increased, the size of, for example, a camera module including the image sensors may be reduced, and a camera phone including the camera module may be relatively small and thin.
However, although the number of pixels is increased and the size of each of the pixels is reduced, if the size of a unit cell for detecting each color is less than 1 μm, that is, below the wavelength range of visible light, resolution is no longer increased due to an optical limitation caused by light diffraction. That is, resolution is not improved, although the size of each of the pixels is reduced to achieve a high degree of integration. This is referred to as resolution saturation. Accordingly, there is a demand for a method of increasing the number of pixels, without reducing the size of a unit cell to less than 1 μm, in order to improve resolution. Also, once the size of a unit cell is reduced, the area of a region for detecting light in a pixel, referred to as an aperture ratio, is also reduced, thereby lowering light use efficiency.